This invention relates to an apparatus for applying sealant to a bore in a workpiece, and more particularly, to an apparatus for applying sealant to a portion of a rivet bore in a workpiece that is readily adaptable for operation with a device for automatically boring and riveting the workpiece.
Riveted aircraft structures, such as the skin on an aircraft wing, are subject to failure because corrosive materials penetrate along the rivet-skin interface, causing corrosion and possible subsequent failure of the rivet connector and surrounding structure. To prevent corrosive materials from penetrating the rivet-skin interface, sealants and/or primers are applied to a portion of the rivet bore before the rivet is inserted and fastened in the bore.
Mechanical devices for applying sealant to the rivet bore, and specifically to a countersink forming part of the rivet bore, are normally used in connection and coordination with automatic riveting machines that drill a bore and countersink bore in the skin or other workpiece and thereafter insert and fasten the rivet in the bore. Prior art sealant applicators will normally apply excess sealant to the rivet bore, causing sealant material to be squeezed from the bore when the rivet is inserted and thus be deposited on the surface of the workpiece. Even if the problem of excess sealant application is not present, most of the prior art devices will pull a string of adhesive away from the rivet bore as the applicator is withdrawn from the bore. This stringing of the adhesive results in sealant deposition on the surface of the skin. The sealant deposited on the skin must be removed prior to use of the workpiece, requiring extra labor, energy and time to produce a finished structure.
An example of such prior art sealant applicators is described in U.S. Pat. No. 3,904,718, issued to Kuehn on September 9, 1975. The Kuehn applicator utilizes a frusto-conically shaped applicator tip that is shaped to precisely mate with the countersink surface of the workpiece bore. An annular groove is located on the circumference of the conical surface of the applicator tip so that the groove is adjacent the countersink surface when the applicator tip is inserted into the workpiece bore. Sealant is applied to the applicator tip by causing the groove of the applicator tip to engage a bead of sealant carried by a tape. As the tip is rotated when in contact with the tape, sealant is picked up by the applicator tip in the grooved area and excess sealant remaining from the previous cycle is removed from the applicator tip by the tape.
The Kuehn applicator, although representing a significant advance in the art, suffers from several deficiencies. In order to deposit the bead of sealant in the correct position within the countersink in the aperture of the workpiece, the rotational axis of the applicator tip must be exactly aligned with the centerline of the workpiece bore and the conical surface of the applicator tip must mate exactly with the surface of the countersink. Moreover, each applicator tip will only fit into a countersink of given dimensions. A slight misalignment of the applicator tip and the countersink or a slight difference between the angle of the countersink and the conical shape of the applicator tip can result in a misplacement of the bead of sealant within the countersink. Also, when the applicator tip is rotating at high rpms, an incorrect positioning of the applicator tip within the workpiece bore could cause the tip to "jump out" of the countersink. These problems are compounded because it is difficult to manufacture and maintain a drill bit that will create a countersink surface within a workpiece that will precisely mate with the conical shape of the rotating applicator tip. Moreover, because the Kuehn applicator head is not adjustable relative to its base, the entire Kuehn apparatus must be exactly positioned relative to the workpiece and the countersink to insure that the applicator tip will be precisely aligned with the centerline of the workpiece bore. The initial alignment of the Kuehn applicator, as installed with an automatic riveting machine, with respect to the centerline of a pressure foot bushing and with respect to the placement of a bead of sealant on the tape takes a person of ordinary skill in the art about 10 to 20 hours. Additionally, the Kuehn applicator tip must be exactly aligned with respect to the bead of sealant placed on the moving tape. A slight mismatch between the bead of sealant on the tape and the groove on the applicator tip causes an insufficient amount of sealant to be placed within the groove of the applicator tip and a corresponding inadequate amount of sealant applied to the countersink, resulting in an inadequate seal of the rivet.
Furthermore, because an automatic riveting machine is constantly vibrating, minor alignment adjustments must be made to the applicator tip. Since the entire Kuehn apparatus must be readjusted to maintain correct alignment, the entire riveting sealing operation must be stopped for a relatively long period to correct the tip alignment, resulting in a significant loss of productive work time. Also, when a Kuehn applicator tip is changed to correspond to different countersink angles and diameters, the groove of the applicator tip must again be aligned with the bead of sealant on the tape.
The sealant supply mechanism disclosed by Kuehn has also been a source of problems. In Kuehn a sealant metering orifice is in fluid communication with a sealant supply source. When the tape moves past the metering orifice, the metering orifice forms a bead of sealant on the tape. The bead of sealant is then transferred to the groove in the applicator tip and excess sealant on the tip is removed by the tape. The tape transfer sealant supply system is unduly complicated and unreliable. Excess sealant cleaned from the applicator by tape is wastefully discarded with the tape. The problem of aligning the applicator tip with the bead of sealant on the tape has been discussed above. Additionally, the feed mechanism must be adjusted to align the tape with respect to the metering orifice to insure that the bead of sealant is correctly positioned on the tape. Also, the metering orifice is rather inaccessably located within the apparatus and therefore difficult to clean. For these reasons the Kuehn sealant applicator, and other devices and methods known as a part of the prior art have not been satisfactory.
It is therefore a broad object of this invention to provide an improved, simplified apparatus for placing an annular bead of sealant material on the wall of the workpiece bore.
A second object of this invention is to provide a sealant applicator that includes an applicator tip which is adjustably positionable with respect to the centerline of a workpiece bore so that during use of the applicator, minor alignment corrections can easily be made.
It is another object of this invention to provide a sealant applicator that will pick up an annular bead of sealant from a sealant supply and apply the bead to a workpiece bore without being precisely aligned either with respect to the sealant supply or the bore.
It is yet another object of this invention to provide a sealant applicator having an uncomplicated and durable sealant supply mechanism.
It is another object of this invention to provide a sealant applicator that will minimize the waste of sealant.
It is still another object of this invention to provide a sealant applicator which minimizes stringing of sealant.